Can i wire a speaker output from my amplified stereo system to an adruino uno to make xmass led lights turn on and off via the uno outputs. Thx for the help
Yes, you can do that.
Run the audio signal into an analog input, and from there your software can activate outputs based on the signal level, or frequency content,* etc.
Since audio signals are AC and the Arduino can be damaged by negative voltages, the Arduino is usually [u]biased at 2.5V[/u].
If your stereo has "tape" outputs, that's an ideal signal level and the tape output doesn't depend on the volume control.
If you need to use the speaker outputs and you'll probably need [u]protection diodes[/u] and possibly a [u]voltage divider[/u] to knock-down the voltage.
- Frequency filtering can be tricky, but there a couple of ways to do it. I suggest you start-out with something simpler... I've built a few lighting effects, and I have lots of interesting variations with only the loudness and "the beat".
If you are also wanting a program then that is not a trivial project. The program needs to be based on frequency or level. Both require different programming.
You have given no information on what you want to do with the LEDs.
Weedpharma
Thank you for your input. My end goal is to have the strand of Christmas lights flash to the beat of the music.
"2 music" did you mean "to music"? Why not say so? It's only one more key press.
Russell.
emmajeff:
Thank you for your input. My end goal is to have the strand of Christmas lights flash to the beat of the music.
Is this a project for next xmas? 
Weedpharma
Yes, i was given an adruino uno board for Christmas. So I've been playing with it turning strands of led lights on and off. So i figured it would be neat to put music it to it. I'm quite new at this but having fun learning.